UCSF

Background

Prolongation of the QT interval has been associated with an increased risk of developing atrial fibrillation (AF), but the responsible mechanism remains unknown.

Objectives

The aims of this study were to subdivide the QT interval into its components and identify the resultant electrocardiographic interval(s) responsible for the association with AF.

Methods

Predefined QT-interval components were assessed for association with incident AF in the Atherosclerosis Risk in Communities study using Cox proportional hazards models. Hazard ratios (HRs) were calculated per 1-SD increase in each component. Among QT-interval components exhibiting significant associations, additional analyses evaluating long extremes, defined as greater than the 95^th percentile, were performed.

Results

Of the 14,625 individuals, 1505 (10.3%) were diagnosed with incident AF during a mean follow-up period of 17.6 years. After multivariable adjustment, QT-interval components involved in repolarization, but not depolarization, exhibited significant associations with incident AF, including a longer ST segment (HR 1.27; 95% confidence interval [CI] 1.14-1.41; P < .001) and a prolonged T-wave onset to T-wave peak (T-onset to T-peak) (HR 1.13; 95% CI 1.07-1.20; P < .001). Marked prolongation of the ST segment (HR 1.31; 95% CI 1.04-1.64; P = .022) and T-onset to T-peak (HR 1.36; 95% CI 1.09-1.69; P = .006) was also associated with an increased risk of incident AF.

Conclusion

The association between a prolonged QT interval and incident AF is primarily explained by components involved in ventricular repolarization: prolongation of the ST segment and T-onset to T-peak. These observations suggest that prolongation of phases 2 and 3 of the cardiac action potential drives the association between the QT interval and AF risk.